WHAT IS STEEL?
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| In the beginning, there was iron... |
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Iron is one of the most common metals
in the earth's crust. It can be found almost everywhere,
combined with many other elements, in the form of
ore. In Europe, iron working dates back to 1700
B.C.
From the time of the Hittites to the end of the
Middle Ages, the preparation of iron remained the
same: alternating layers of ore and wood (or charcoal)
were heated until a mass of molten ore was obtained,
which it was then necessary to hammer while hot
in order to remove the impurities - and thereby
obtain the raw iron, ready to be forged. The forge
was set up a few steps away from the hearth where
the metal was prepared.
Originally a simple conical hole in the ground,
the hearth became a furnace, the "low forge,"
and was gradually perfected: from a few kilograms
at first, the quantity of iron that could be obtained
had risen to 50 to 60 kilograms by the Middle Ages.
Moreover, small quantities of steel, i.e., iron
enriched with carbon, were manufactured from the
beginning. This material proved to be both harder
and more resistant. |
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| Then came cast iron... |
In the 15th century, construction
of the first "high forges" (the precursors
of the blast furnace) 4 to 6 meters in height resulted
in a lucky but major discovery: a ferrous metal
in liquid form, cast iron, which was used to manufacture
all types of objects (cooking pots, cannon balls,
andirons, pipes, etc.).
Cast iron also allowed iron to be produced in quantity,
through refining: an ingot of cast iron was heated
and air blown over it, causing the carbon in the
cast iron to burn and the iron to run off drop by
drop, forming a molten mass of raw iron. |
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| ...and finally steel |
| In 1786 Berthollet, Monge and Vandermonde, three French
scientists, precisely defined the nature of the Iron/Cast
Iron/Steel relationship and the role of carbon in the
preparation and characteristics of these three materials*. |
| However, it wasn't until the great inventions of the
19th century (the Bessemer, Thomas and Martin furnaces)
that steel, up to that point manufactured from iron in
small quantities, experienced spectacular growth and quickly
became the most important metal of the industrial revolution.
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| At the beginning of the 20th century, world steel production
totaled 28 million tons, i.e., six times more than in
1880. By the beginning of World War I, it totaled 85 million
tons. Within a few decades, steel had powerfully strengthened
the equipment used in manufacturing and had replaced iron
in most applications. |
| Steel, a metal of many uses |
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There are two major families of steel:
alloy steels and non-alloy steels. Alloy refers
to chemical elements other than carbon added to
the iron in accordance with a minimum variable content
for each.
For example: 0.50% for silicon, 0.08% for molybdenum,
10.5% for chrome. Thus an alloy of 17% chrome and
8% nickel is used to create stainless steel. It
is for this reason that there is not one but many
types of steel.
Currently there are over 3,000 catalogued grades
(chemical compositions), not counting those created
to meet custom demand, all of them contributing
to making steel the most appropriate material for
meeting the challenges of the future. |
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Next: How is steel made? |
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